As is well known in the gas turbine engine technology the modern day fighter aircraft incorporate thrust vectoring nozzles that include variable positioning flaps that direct the engine's exhaust to flow at various attitudes. It is also well known that the throat of the exhaust nozzle is varied from a minimum to a maximum area to accommodate certain fight conditions. The problems that have perplexed the scientists and engineers in this technology is the cooling of the components that are in contact with the hot engine discharge gasses without incurring an intolerable performance deficit.
In heretofore known exhaust nozzles, designs ram air is applied to the hot surface defining the boundary of the gas path of the divergent nozzle by flowing engine ram air through a relatively large ejector slot located adjacent the throat of the exhaust nozzle. While this design intended to distribute film air adjacent the inner surface of the divergent portion of the nozzle, because of the configuration of the ejector which is dictated by the amount of cooling required and hence the amount of cooling air, these systems were not only costly in terms of the amount of cooling air required, but the overall cooling effectiveness was less than satisfactory. In other words the heretofore known designs exhibited the following disadvantages;
1) Cooling air discharges at high gas path pressure region induces high viscous mixing with a consequential reduction in film cooling effectiveness. PA1 2) At high gas path pressure region, the ejector slot has to overcome a high base pressure, resulting in a reduction of pumping efficiency, requires a large slot size and/or in some cases the loss of ejection of cooling air. PA1 3) In a vectoring nozzle application, due to the nozzle throat shifting for the different attitudes of the nozzle, hot gas injection could occur during the vectored mode.
We have found that we can obviate the problems noted above by providing a cooling extension for the ejector of a liner cooling system that allows the low pressure ram air to be discharged further downstream of the nozzle to a lower nozzle pressure region. This produces a lower slot base pressure, enhances pumping capability and reduces slot size requirement. This invention enhances film cooling which is controlled by the supersonic primary stream expansion and recompression characteristics induced by the aft facing ejector slot. The expansion and recompression is minimized when the secondary stream pressure (ram air) is approximately balanced or "matched" with the primary stream (gas path) "approach" static pressure. Matching these pressures creates a co-annular flow situation with little near wall influence from the primary stream and minimal film decay over the cooled length.
Essentially the cooling extension of the ejector cooling system of this invention minimizes turbulent mixing between the streams and hence enhances the pumping, cool film effectiveness and engine thrust. By configuring the slot edge shapes of the cooling extension an improvement in infrared detection is realized.
In certain applications the cooling extension with a fixed ejector slot may present certain problems in that at the off-design points the cooling flowrate capability may not respond to demand. For example, at maximum augmentation in the augmentor of the engine, when the nozzle throat area is increased the cooling slot-to-throat (slot of the ejector and throat of the nozzle) area ratio is reduced, resulting in a reduction of cooling flow pumping capability and film effectiveness level. This has a consequential impact on the temperature and could cause an overtemperature situation in the nozzle with a potential damage or life limiting of the component parts. We have found that we can obviate the problem described in the immediate above paragraph by incorporating a vane cooperating with the ejector slot and being varied as a function of the nozzle throat area (Aj).